Using ECMWF's 45-year ERA40 global reanalyses on a 2.5 by 2.5 degree grid, we composite mid-latitude weather events based on a particular vorticity threshold. The composites are centered in time on the occurrence of 50 kPa vorticity maxima at (55W, 50N) off the east coast of North America. Similar composites are prepared centered on times of 50 kPa vorticity maxima at (137.5E, 42.5N) off the east coast of Asia.

With the ERA40 providing not just vorticity, but all standard variables at multiple levels, these variables can be composited, centered at the same times as the vorticity maxima. By compositing 10 days prior to and after the vorticity maxima, we examine the three-dimensional structure of the global antecedents and consequences of mid-latitude synoptic-scale systems. By removing the annual cycle of the atmosphere, the upstream and downstream consequences on a global scale of these events are revealed more clearly. Oscillations and patterns are essential in weather forecasting, and such analyses showing relations in weather phenomena can improve weekly weather forecasts.